Technical Field
The present disclosure relates to an aluminum alloy conductor used as a conductor of an electric wiring structure, and particularly relates to an aluminum alloy conductor that provides high conductivity, high bending fatigue resistance, and also high elongation, even as an extra fine wire.
Background
In the related art, a so-called wire harness has been used as an electric wiring structure for transportation vehicles such as automobiles, trains, and aircrafts, or an electric wiring structure for industrial robots. The wire harness is a member including electric wires each having a conductor made of copper or copper alloy and fitted with terminals (connectors) made of copper or copper alloy (e.g., brass). With recent rapid advancements in performances and functions of automobiles, various electrical devices and control devices installed in vehicles tend to increase in number and electric wiring structures used for devices also tends to increase in number. On the other hand, for environmental friendliness, lightweighting is strongly desired for improving fuel efficiency of transportation vehicles such as automobiles.
As one of the measures for achieving recent lightweighting of transportation vehicles, there have been, for example, continuous efforts in the studies of changing a conductor of an electric wiring structure to aluminum or aluminum alloys, which is more lightweight than conventionally used copper or copper alloys. Since aluminum has a specific gravity of about one-third of a specific gravity of copper and has a conductivity of about two-thirds of a conductivity of copper (in a case where pure copper is a standard for 100% IACS, pure aluminum has approximately 66% IACS), a pure aluminum conductor wire rod needs to have a cross sectional area of approximately 1.5 times greater than that of a pure copper conductor wire rod to allow the same electric current as the electric current flowing through the pure copper conductor wire rod to flow through the pure aluminum conductor wire rod. Even an aluminum conductor wire rod having an increased cross sectional area as described above is used, using an aluminum conductor wire rod is advantageous from the viewpoint of lightweighting, since an aluminum conductor wire rod has a mass of about half the mass of a pure copper conductor wire rod. Note that, “% IACS” represents a conductivity when a resistivity 1.7241 ×10−8 Ωm of International Annealed Copper Standard is taken as 100% IACS.
However, it is known that pure aluminum, typically an aluminum alloy conductor for transmission lines (JIS (Japanese Industrial Standard) A1060 and A1070), is generally poor in its durability to tension, resistance to impact, and bending characteristics. Therefore, for example, it cannot withstand a load abruptly applied by an operator or an industrial device while being installed to a car body, a tension at a crimp portion of a connecting portion between an electric wire and a terminal, and a cyclic stress loaded at a bending portion such as a door portion. On the other hand, an alloyed material containing various additive elements added thereto is capable of achieving an increased tensile strength, but a conductivity may decrease due to a solution phenomenon of the additive elements into aluminum, and because of excessive intermetallic compounds formed in aluminum, a wire break due to the intermetallic compounds may occur during wire drawing. Therefore, it is essential to limit or select additive elements to provide sufficient elongation characteristics to prevent a wire break, and it is further necessary to improve impact resistance and bending characteristics while ensuring a conductivity and a tensile strength equivalent to those in the related art.
Japanese Laid-Open Patent Publication No. 2012-229485 discloses a typical aluminum conductor used for an electric wiring structure of transportation vehicle. Disclosed therein is an extra fine wire that can provide an aluminum alloy conductor and an aluminum alloy stranded wire having a high strength and a high conductivity, as well as an improved elongation. Also, Japanese Laid-Open Patent Publication No. 2012-229485 discloses that sufficient elongation results in improved bending characteristics.
However, in the aluminum alloy conductor disclosed in Japanese Laid-Open Patent Publication No. 2012-229485, for example, when used as a wire harness attached to a door portion, fatigue fracture is likely to occur due to repeated bending stresses exerted by opening and closing of the door, and it cannot be said that bending fatigue resistance under such severe operating environment is sufficient. Further, assuming that it is attached to an engine portion, for example, a diesel engine which is said to produce a greatest vibration, a higher bending fatigue resistance which is capable of withstanding a constantly produced engine vibration is required.
The present disclosure is related to providing an aluminum alloy conductor, an aluminum alloy stranded wire, a coated wire, and a wire harness and to provide a method of manufacturing aluminum alloy conductor that can ensure a high conductivity and also achieve a high bending fatigue resistance, a high impact absorption and a high elongation, simultaneously.
The present inventors have found that with an uneven grain size in an aluminum alloy conductor, a portion in which the grain size is large has a lower strength and is likely to be deformed, an elongation of an aluminum alloy conductor as a whole decreases. Also, present inventors have found that in a case where the grain size is large, an accumulated amount of plastic strain is greater than a case in which the grain size is small, and a bending fatigue characteristics decreases. Thus, the present inventors have focused on the fact that a grain growth can be suppressed by introducing compound particles into an aluminum alloy. The present inventors carried out assiduous studies and found that by uniformly dispersing compound particles in an aluminum alloy conductor, crystal grains of an appropriate size are evenly formed, and thus a high bending fatigue resistance is obtained and an appropriate proof stress and a high elongation are further achieved, while ensuring a high conductivity, and contrived the present disclosure.